Pair Of Pro Duo for a Blender workstation
I have a Pro Duo and I don't see why two of them can't work together. With 2 cards, you'll have access to 4 compute devices since each card has 2 GPUs.

Checklist:


These cards a really long, make sure your case can fit them.
These cards are 250W each, so make sure you have a 750Watt+ power supply. Also, they require a set of 6+8pin PCIE power connectors for each GPU.


The rendering performance will scale very linearly with additional GPUs. But keep in mind that you are still limited to 16GB of video memory(per GPU), not the combined total video memory (64GB).